Opioids may affect the part of the brain that mediates feelings of pleasure. As a result, people who take these medications often experience feelings of euphoria that can lead to addiction in some users. Patients with a history of psychological problems or substance abuse have a greater risk for opioid addiction.

Opioid medications rarely cause addiction when used correctly under a physician’s close supervision for acute pain and cancer pain. However, there is a risk of addiction, which is also called psychological dependence, when opioids are used to treat chronic pain, even in patients with no history of drug abuse. 

People who use opioids over an extended period may develop two conditions that are often confused with addiction: tolerance and physical dependence. Neither of these is a form of addiction.

Chronic use of opioids may result in the user developing a tolerance to the drug. When this occurs, increasingly higher amounts of the opioid are required before the user obtains the same initial effect.

Physical dependence may occur in patients who use opioids for more than a few weeks. When a person’s body becomes dependent upon an opioid, the body requires the substance to avoid going into withdrawal. To avoid withdrawal, patients need to gradually taper off using opioids rather than quitting them “cold turkey.” Symptoms of withdrawal associated with opioids include:

• Restlessness
• Muscle pain and bone pain
• Insomnia
• Diarrhea
• Vomiting
• Cold flashes (including associated “goose bumps”)
• Involuntary leg movements

Use of opioids also may cause patients to experience other side effects. Some of the more common side effects include:

• Drowsiness
• Constipation
• Itching
• Mild dizziness, lightheadedness or fainting
• Unclear thinking
• Nausea and vomiting
• Dry mouth
• Sedation
• Decreased levels of the hormone testosterone, causing reduced sex drive
• Cardiovascular effects, such as accelerated heart rate
• Depression of respiration and cough reflex
• Gastrointestinal disorders
• Decreased motor response rate
• Urinary retention

In addition, opioids slow activity in the respiratory center of the brainstem. If taken in high doses, opioids can cause severe respiratory distress and may even result in death. If opioids are used for an extended periods they can actually increase pain. This condition is known as hyperalgesia. The mechanism that causes this is unclear. The current thinking is that it may be due to the effects of opioids on chemical receptors in the brain.

Patients should seek immediate medical care if they experience any of the following more serious side effects related to opioids:

• Extreme restlessness or nervousness
• Confusion
• Dizziness
• Severe weakness
• Extreme drowsiness
• Cold, clammy skin
• Breathing difficulties
• Low blood pressure
• Slow heartbeat
• Convulsions
• Constricted pupils (miosis)